Near-infrared absorptive dyes are used for various purposes in wide fields. The dyes are used in, for example, infrared-cutting films for plasma display panels (PDP) or CCDs, optical filters in heat ray shield films, or photothermal conversion materials in write once optical disks (CD-R) or flash-meltable and fixable materials. Moreover, the dyes are used as information displaying materials for security inks or invisible bar code inks. For near-infrared absorptive dyes, it is very important that the dyes are excellent in invisibility, i.e., the property that the dyes are invisible, as well as the dyes show an intense absorption for rays in the near infrared range. Furthermore, for all dyes, a high durability (fastness) is required.
As dyes which hardly show an absorption in the wavelength range of 400 to 700 nm and are excellent in invisibility, cyanine methine dyes or J associations thereof can be mentioned. However, their long methine conjugated chain is flexible; thus, the dyes are easily isomerized so that the absorption wavelengths are changed, or the dyes are easily decomposed by heat or by reaction with oxygen or a nucleophilic agent. Accordingly, the dyes are low in fastness.
As near-infrared absorptive dyes having a rigid skeleton and a high fastness, there are vanadylnaphthalocyanine dyes suggested by Nippon Shokubai Co., Ltd., and quaterrylene dyes marketed by BASF AG. However, vanadylphthalocyanine dyes are insufficient in invisibility. The quaterrylene dyes have good invisibility in a state of molecular dispersion, for example, in a state of a solution of the dyes; however, when the concentration is made high, an absorption is generated for rays in the visible range by the association of the molecules so that the invisibility is lost. Thus, the way of use thereof is restricted.
As dyes that are excellent in invisibility and have an absorption for rays in the infrared range widely, there are diimmonium dyes marketed by Nippon Kayaku Co., Ltd. However, the dyes are easily reducible and are insufficient in fastness. Thus, the way for use thereof is restricted.
As described above, near-infrared absorptive dyes having both excellent invisibility and fastness have not been marketed up to date. Thus, it has been desired to develop near-infrared absorptive dyes having these performances compatibly with each other.
Further, pyrrolopyrrol dyes are known as a novel infrared absorptive dye (see, for example, Non-Patent Document 1). The Non-Patent Document 1 describes the results from a study on application of the pyrrolopyrrol dye to an infrared fluorescent dye. More specifically, the Non-Patent Document 1 describes that high-fluorescence quantum yield can be achieved by complexation of the pyrrolopyrrol dye with boron and by enhancing rigidity of the molecule. As an application for the fluorescent dye characteristic to this skeleton group, application to organic electroluminescent devices is known (see, for example, Patent Documents 1 to 3).
Generally, in order to emit high fluorescence, a fluorescent dye is used in such a dilute state that concentration quenching is not caused, and further the fluorescent dye is co-deposited with a host material and used in a molecular dispersion state. Further, it is known that such fluorescent dye generally shows low resistance to light.    [Patent Document 1] Japanese Patent No. 3704748    [Patent Document 2] JP-A-2003-027049 (“JP-A” means unexamined published Japanese patent application)    [Patent Document 3] WO2003/048268    [Non-Patent Document 1] Angewante Chemie International Edition of English, Vol. 46, pp. 3750 to 3753, 2007